http://weather.unisys.com/gfsx/index.php?r=us
The trough / ridge pattern can be used
as a medium range-forecasting tool. If the GFS model has a good handle on the evolution of the
trough / ridge pattern, the forecast will do reasonably well. Keep in mind that beyond about 5 days, the
GFS data output can change quite dramatically from one model run to the other. Small changes in the initial
input into the model result in dramatic difference beyond the 5 day forecast period (i.e. butterfly effect).
The trough / ridge pattern determines which regions will be cooler or warmer than normal and which regions
have
a higher likelihood of precipitation. Temperatures tend to be cooler than normal under amplified troughs
and warmer than normal under amplified ridges. Precipitation tends to occur to the right of a highly
amplified trough axis, along fronts and along
shortwaves. The graphical output visual appearance from
the GFS is similar to the NAM.